(1) Field of the Invention
The present invention relates to methods for the delivery of charge material to the interior of a shaft furnace and to apparatus for use in the practice of such methods. More specifically, this invention is directed to charging installations for blast furnaces and particularly to apparatus for delivering the raw material with which a furnace is to be charged to a rotary distribution chute positioned within the furnace. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
One of the most significant recent advances in blast furnace technology is the charging installation known in the art as the "bell less top". The "bell less top" is disclosed in U.S. Pat. No. 3,693,812. Reference may also be had to U.S. Pat. Nos. 3,929,240, 4,042,130, 4,071,166 and 4,074,816. The "bell less top" charging installation employs a rotary and angularly adjustable distribution chute which, prior to the present invention, has been supplied with material from a pair of intermediate storage hoppers. The success of the "bell less top" charging system is attributable to the fact that, by enabling the charging process to be more accurately controlled than has previously been possible, it has permitted the operating limits of furnaces which would otherwise have been equipped with conventional bell-type charging devices to be exceeded. The significant increase in the degree of control which may be exercised over the operation of a blast furnace with a "bell less top" allows furnace output to be optimized.
For further description of the construction and operation of the "bell less top", reference may be had to the aforementioned patents.
As noted above, prior "bell less top" charging installations have been characterized by a pair of juxtapositioned intermediate storage hoppers which were alternately placed in communication with the interior of the furnace, and thus the charge distribution chute, by apparatus which includes a material flow control or dosing valve. Isolation valves were also provided at both the feed and discharge ends of the intermediate storage hoppers since the hoppers must alternately be at atmospheric pressure to permit loading and at furnace pressure to permit discharging. The use of a pair of intermediate storage hoppers enables the charging of the furnace to proceed on an essentially continuous basis; the only interruptions necessitated being during the opening and closing of the isolation valves. Thus, in accordance with prior "bell less top" technology, a plurality of intermediate storage hoppers are employed and one storage hopper was filled while another was discharging its contents into the furnace. This results in the significant advantage that the productivity of the furnace is not limited by the charging installation.
The "bell less top" charging installations of the referenced patents, while unquestionably highly desirable for employment on modern large-capacity furnaces, are somewhat less cost effective for medium and small capacity blast furnaces. Further, both equipment costs and installation costs must be taken into account should it be desired to retrofit an existing furnace with a "bell less top" so as to upgrade the furnace. Thus, where an existing blast furnace is to be modernized by replacement of a bell-type charging installation with a "bell less top", the furnace operator must take into account the cost of the new apparatus and also the expenses which may be incurred in fitting the new apparatus to his existing furnace. The modernizing expense will, of course, include the cost of converting or modifying existing equipment such as the apparatus for conveying the charge material to the furnace, the super-structure which includes the bell tower, the foot bridges, etc. All of these expense factors have often worked to prevent the upgrading of existing furnaces by replacing their charging installations with charging apparatus of the "bell less top" type and have also resulted in decisions not to employ the "bell less top" on small and medium capacity blast furnaces.